It's All Your Fault! EarthCache
Hidden : 4/22/2018
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:


This is an Earthcache located along U.S. Highway 63, about four and a half miles south of Vienna. While there is good parking along the side of the road, as there is a wide shoulder, if you have little ones with you, keep an eye on them because the highway can be busy at times!
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As one travels down Highway 63 south of Vienna, several road cuts present themselves. Various geological tales are told, but what one might not know is that one tale, the tale of faults, is also related in this area. Famous faults, like the San Andreas Fault and even the historical faults that lie below New Madrid, Missouri, are well known. What isn't so well known is that faults dot the landscape all over our great state of Missouri. Let's learn about them.

What are faults?

A fault a planar or gently curved fracture in the rocks of the Earth’s crust, where compressional or tensional forces cause relative displacement of the rocks on the opposite sides of the fracture. Faults range in length from a few inches to many hundreds of miles, and displacement likewise may range from less than an inch to several hundred miles along the fracture surface (the fault plane). In some instances, the movement is distributed over a fault zone composed of many individual faults that occupy a belt hundreds of yards wide. The geographic distribution of faults varies; some large areas have almost none, others are cut by innumerable faults.

Faults may be vertical, horizontal, or inclined at any angle. Although the angle of inclination of a specific fault plane tends to be relatively uniform, it may differ considerably along its length from place to place. When rocks slip past each other in faulting, the upper or overlying block along the fault plane is called the hanging wall, or headwall; the block below is called the footwall. The fault strike is the direction of the line of intersection between the fault plane and the surface of the Earth. The dip of a fault plane is its angle of inclination measured from the horizontal.

Faults are classified according to their angle of dip and their relative displacement. There are three main types...

Normal dip-slip faults are produced by vertical compression as the Earth’s crust lengthens. The hanging wall slides down relative to the footwall. Normal faults are common; they bound many of the mountain ranges of the world and many of the rift valleys found along spreading margins of tectonic plates. Rift valleys are formed by the sliding of the hanging walls downward many thousands of yards, where they then become the valley floors. A block that has dropped relatively downward between two normal faults dipping toward each other is called a graben. A block that has been relatively uplifted between two normal faults that dip away from each other is called a horst. A tilted block that lies between two normal faults dipping in the same direction is a tilted fault block.

Reverse dip-slip faults result from horizontal compressional forces caused by a shortening, or contraction, of the Earth’s crust. The hanging wall moves up and over the footwall. Thrust faults are reverse faults that dip less than 45°. Thrust faults with a very low angle of dip and a very large total displacement are called overthrusts or detachments; these are often found in intensely deformed mountain belts. Large thrust faults are characteristic of compressive tectonic plate boundaries, such as those that have created the Himalayas and the subduction zones along the west coast of South America.

Strike-slip faults are similarly caused by horizontal compression, but they release their energy by rock displacement in a horizontal direction almost parallel to the compressional force. The fault plane is essentially vertical, and the relative slip is lateral along the plane. These faults are widespread. Many are found at the boundary between obliquely converging oceanic and continental tectonic plates. A well-known terrestrial example is the San Andreas Fault, which, during the San Francisco earthquake of 1906, had a maximum movement of about 20 feet.

Fault slip may polish smooth the walls of the fault plane, marking them with striations called slickensides, or it may crush them to a fine-grained, claylike substance known as fault gouge; when the crushed rock is relatively coarse-grained, it is referred to as fault breccia. Occasionally, the beds adjacent to the fault plane fold or bend as they resist slippage because of friction. Areas of deep sedimentary rock cover often show no surface indications of the faulting below.

Movement of rock along a fault may occur as a continuous creep or as a series of spasmodic jumps of a few yards during a few seconds. Such jumps are separated by intervals during which stress builds up until it overcomes the frictional forces along the fault plane and causes another slip. Most, if not all, earthquakes are caused by rapid slip along faults.
SOURCES CITED

Geologic Wonders and Curiosities by Thomas R. Beveridge,
Second Edition, revised by Jerry D. Vineyard, 392 p., 163 figs., app., 1991.

Roadside Geology by Charles G. Spencer, 274 p., 2011.

The Editors of Encyclopaedia Britannica. 2017 June 5th. "Fault". Retrieved from https://www.britannica.com/science/fault-geology
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To log this Earthcache, please email me the answers to the following questions. Any logs that do not follow these requirements will be quietly deleted.

1. Using your own words, explain how you can visually tell that this is a fault, instead of a simple crack?

2. What type of fault do you see here?

3. Estimate the distance the rock layers have been displaced. Use the larger, top layer as a reference.

4. From the ground to the top of the rock ledge, measure or estimate the length of the visible fault line.

5. What type of fault is the San Andreas fault?
While completely optional and not required, it would be nice to post a photo of yourself with fault behind you.


Additional Hints (No hints available.)



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